skema soalan final v.2 - bfc315332603

8/12/2019 Skema Soalan Final v.2 - BFC315332603

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FINAL EXAMINATION

SEMESTER II

SESSION 2011/2012

COURSE NAME : MECHANICAL & ELECTRICAL SYSTEM

Q1 (a) Discuss on the importance of Mechanical and Electrical System for high

rise building. Give at least three (3) main reasons.(6 marks)

Answer:1. High-speed building vertical transportation helps to conveys peoples/building occupants

from one level to the other levels faster than using stairs in high rise buildings. (2m)

2. High pressure water system is needed to supply water for drinking and cleaning purposesand also as protection against fire at the higher levels. (2m)

3. HVAC system helps to keep the building occupants stays at a comfort level because as thebuilding height increase, it is impossible for the building occupants to rely on natural

ventilation due to high wind pressure at the external environment. (2m)

(b) Explain the process of heat transfer through conduction, convection

and radiation in terms of definition, medium and transfer method.

Conduction Convection Radiation

Medium material liquid/gas vacuum/fluid/gas

Methodmolecular

agitation

fluid

movementby photon

Definition as below as below as below


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(9 marks)

(c) A certain un-insulated cavity wall has a U-value of 0.85W/mK. If

insulation board is added to the construction, where the thickness of

this board is 0.40mm, calculate the percentage reduce for the U-value.

Given that the thermal conductivity of the insulation board is

0.025W/mK.

Step Calculation

Thickness of material, d 0.04m

Thermal conductivity of insulation board, k @ 0.025

k-value of proposed insulating material is k=0.025

Use formula involving thickness of material d, so

the value of Rib

Rib= d/k so,

Rib=0.04/0.025

Rib=1.6

Given R1=1/U1Calculate R1

R1=1/0.85 so,

R1=1.176

Calculate R2 Rib=R2-R1so,

R2= Rib+ R1R2=1.6+1.176

R2=2.776

U-Value U2=1/R2

Calculate proposed U2

U2= 1/2.776

U2= 0.36

Percentage reduce

(U1-U2)/U1x10057.65%

(10 marks)


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When the air supplyis controlled mechanically and the air exhaust takes place on a

natural way by ventilation openings, windows or shafts there will be an overpressure

in the building.

To prevent draught, the air supply in the room has to be placed as high as possibleand

the air inlet grid must have a possibility to be regulated.

By preheating the incoming air draught problems can also be decreased. An air filter

can be usedto clean the incoming air. A ventilator controls the air supply and the

outdoor air is transported into the building by ducts.

Because of the mechanically produced over pressure in the building, the system is less

dependent on the weather conditions than a fully natural ventilation system. By

controlling the ventilator it is possible to control the ventilation capacity of the

system.

In a supply system,a fan pulls outside air into the house, creating positive pressure.

Ductwork brings the air into the living spacesthat need it most typically the

bedrooms and living room.

Balance system

Or

A balanced central system uses two fansand creates a neutral or balanced pressure.

One fan exhausts air out of the house, while the other brings the same amount of

outside air into the house.


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They may be two wall-mounted fansof equal capacity--one for supply and one for

exhaust--in two different rooms.

Alternatively, they may be ducted to supply air to the common living areas, such as

living rooms and bedrooms, and to exhaust air from the rooms where pollution is

high, such as the kitchen and bathroom.

In a balanced system, airis supplied to some rooms and exhausted from others. An

optional heat- or energy-recovery unit transfers heat or humidity from one air stream to

the other. Spot exhaust is included where necessary; here it is in the laundry room

Plenum System

Or

Plenum is the space that can facilitate air circulationfor heating and air conditioning

systems, by providing pathways for either heated/ conditioned or return airflows.

Spacebetween the structural ceiling and the dropped ceiling or under a raised floor istypically considered plenum.


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Population percentage at 5 min peak demand period = 17%

Floor height = 3.3 metres

(6 marks)

1. Flow rate allowing 17% of population

950017 =161.5 persons during 5 min peak demand period10100 (2 Marks)

2. Travel & speed

Assuming floor height of 3.3m, the lift travel = 19 3.3=62.7 From table, thenearest travel for offices is 60m which requires speed of 3.5m/s. (Groundfloor is not included)

(2 Marks)


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3. Number and capacity of lift

From table, for 20-passenger cars may be installed having a handling capacity of165 and interval of 29s (1 Marks)

.4. Quality of service

From table interval 29s ---satisfactory waiting time of 25-35 s (excellent)5 lift / 20 storeys ---satifactoryOr more than 5 lift.

(2 Marks)

(c) Define the following:

(i) Passive fire system

(ii) Active fire system

Then, list down three (3) of the fire hazard categories with example of suitable

fire fighting agents each.(7 marks)

c) Definition:

1) Passive fire systemsPassive fire protection ( pfp ) is defines as protection through ignition delays,

reduced rate of burning and fire spread.

Or

Protections through human indirect approach which more focusing on building

designs or architectural works with the purpose to delay the spreading of fire and

fire exit.

2) Active fire systemsActive fire protection (AFP) is AFP is characterized by items or systems, which

require a certain amount of motion and response in order to work, contrary to

passive fire protection.

4 Fire Hazard categories


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(d) In the fire hydrants system, it consists of using hose reel and riser and

generally the type of riser can be either wet, dry or foam riser. With the

help of sketches, explain how the wet and dry riser works.(8 marks)

d)

Dry riser system Wet riser system

( 1 marks for each sketches)

Dry riser system.

The riser system is maintained in dry condition during non-fire condition.

The riser must always be inspecting to prevent the case of corrosion.

It use direct supply approach where the source of water is from water main pipe

outside the building or hydrants.

Class Type of Fire Fire Fighting Agent

AFires that involve flammable solids such as wood, cloth,rubber, paper, and some types of plastics

Water, Dry Chemical Powder, Foam

B

Fires that involve flammable liquids or liquifiable solidssuch as petrol/gasoline, oil, paint, some waxes &plastics, but notcooking fats or oils AND Fires thatinvolve flammable gases, such as natural gas,hydrogen, propane, butane

CO2, Dry Chemical Powder, Foam,

Halon

C

Fires that involve any of the materials found in Class Aand B fires, but with the introduction of an electricalappliances, wiring, or other electrically energizedobjects in the vicinity of the fire, with a resultantelectrical shock risk if a conductive agent is used tocontrol the fire

CO2, Dry Chemical Powder, Halon

DFires that involve combustible metals, such as sodium,magnesium, and potassium

Dry Chemical Powder


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The riser must be connecting to the outdoor hydrants to get the water.

Usually the system will be activate/ assembled by fire brigade.

This system is slower than wet riser system in providing water.

Wet riser system

It uses indirect supply approach which the source of water is from the storage

tank.

The riser is always filled with water and can be used immediately during fire

occurrence.

Maintenance must be done to check for the leaking pipe.

This system using pump to distribute the water.

The source of water depends on the storage tank capacity.

Q4 (a) Explain briefly the following electrical terms:

(i) Current (I)

An electric current is the flow of electric charges. Conventionally this is the flow of positive charge. In a simple circuit such as that illustrated, the current in the wire is composed of

electrons that flow from the negative pole of the battery (the cathodeat the bottom

of the battery) and return to the positive pole (the anodeat the top of the battery,

marked by a +).

Electric current is the time rate of change of charge, measured in amperes (A). Mathematically, the relationship between current i, charge q, and time t, is Where current is measured in amperes (A), and 1 ampere = 1 coulomb/second

(ii) Voltage (V)

Some work or energy transfer is required to move the electron in a conductor in aparticular direction. This work is performed by an external electromotive force

(emf), typically represented by the battery.

The emf is also known as voltage orpotential difference. Electric potential is the energy required to move a unit of electric charge to a

particular place in a static electric field.

Voltage can be measured by a voltmeter. The unit of measurement is the volt.

(iii) Resistance (R)

Is an internal property of matter that resists the flow of electric current. A material with low resistance to electrical flow is called a conductor. A material with a high resistance to electrical flow is called an insulator: paper

rubber.

Electrical conductors are pure metals; aluminum, copper, silver, gold and platinum.

(6 marks)


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(b) Compare the difference between power and energy in electricity

Power Energy

Power is a measure of how fastenergy is being used. (power is the

rate of consuming energy) Power is a certain amount of energy

used in a certain length of time

P = energy/time = W/t

Power is the time rate of expendingor absorbing energy, measured in

watts (W).

Power is the rate of consumingenergy.

Energy is the fundamental ability todo work and produce action.

Energy exists in many forms, suchas mechanical, sound, light,

electrical, nuclear and chemical.

Energy cannot be created ordestroyed. It can be converted from

one form to another.

Energy is measured in joules, but inmany fields other units, such as

kilowatt-hours and kilocalories, are

customary.

Electrical energy is the most

convenient form of energy that isreadily to be convert to other forms.

For examples; to mechanical energy

through a motor, to lighting energy

through a lamp, and to heating

energy through a resistance heater.

(4 marks)

(c) Suppose that two 100 watts lamp and two 200 watts lamp are plugged

into a 240 volt circuit. The two lamps are connected in parallel. Calculate the

current flow through each lamp, the total current in the circuit, the

total resistance of the circuit, the total energy consumed in a year, and the

cost of electrical energy for the year (based on RM1.10 per kWh). Assuming

that the lamps are used 8 hours per day and 250 days per year. All

calculation steps shall be included in your answer.(15 marks)

Current flow through each lamp (4 marks)

P=IxE, I=P/E

I1=100w/240v=0.416A

I2=100w/240v=0.416A

I3=200w/240v=0.833A

I3=200w/240v=0.833A

Total current through the circuit (2 marks)

IT=0.416 x 2 + 0.833 x 2 = 2.498 A/2.5A

Total resistance of the circuit (5 marks)

R=E/I

*resistance of lamps


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R1=240/0.416=576.9/577ohms

R2=240/0.416=576.9/577ohms

R3=240/0.833=288.1/288ohms

R4=240/0.833=288.1/288ohms

Total resistance of the circuit

1/RT=1/577+1/577+1/288+1/288

1/RT=0.0017+0.0017+0.0035+0.0035 = 0.0104

RT=1/0/0104=96.15ohms

Total energy consumed in a year (2 marks)

W=Pxt = (200+200) x 8 x 250 = 800,000Wh=800kWh.

Cost of electrical energy for the year (2 marks)

Cost=energy used x energy rate=600kWh x RM1.10/kWh=RM660,000 per year.

Q5 (a) As an consultant engineer, you are asked to design water storage tank,

suction tank, and supply pipe for discharge of 1.25litres/sec,

based on gravity supply for Tun Syed Nasir hostel. The hostel are

consists of three (3) blocks of building, each building have 100 rooms

and in each room maximum 4 students can be accommodated. Also

determine the total water requirement for DTI hostel. Assume head

loss is negligible, and length of pipe is 30m allow 20% for bends

and other unforeseen. Assume 91 litres per person of cold water

to cover 24 hours interruption of supply, and disruption of

supply 12 hours.(20 marks)

Answer (a)

Data:

3 building blocks TDI hostel

100 rooms in 1 block of building

4 persons can be accommodated in 1 room

91 lit/day per person per day consumption

Disruption of supply for 12 hours

Effective Length of pipe = 30 m

Discharge of supply pipe = 1.25litres/sec

Head loss = 20% of effective length of pipe


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For practical design assume 4 storage tanks for 1 block of building, therefore each

building block will have to install 3 storage tanks.

Water required to store in 1 tank = 109.33/12 = 9.12 m3

Size of tank is depend upon the choice of student either circular, rectangle, square,however it volume of tank must be greater than the required water volume for storage.

Assume square tank of = 2.1 m x 2.1 m x 3 m (with free board of 0.7m)

o Volume of suction tank = 1/3 x total water requirement

= 1/3 x 164 m3 = 54.66 m3

For practical design assume 3 suction tanks = 54.66/3 = 18.50 m3

Size of tank is depend upon the choice of student either circular, rectangle, square,

however it volume of tank must be greater than the required water volume for storage.

Assume square tank of = 3 m x 3 m x 2.3 m (with free board of 0.3m)

o Diameter of supply pipe can be calculated by Thomas box formula:

(b) Differentiate between water efficiency and water conservation? Enlist

the names of water efficiency approach?(5 marks)

Water efficiency means using improved technologies and practices that deliver equal

or better service with less water. For example, the use of low-flow faucet (A regulator

for controlling the flow of a liquid) aerators can be more powerful than no aerators for

washing hands.

Water conservation has been associated with curtailment of water use and doing

less with less water, typically during a water shortage, such as a drought; for

example, minimizing lawn watering and automobile washing in order to conserve

water. Water conservation also includes day-to-day demand management to better

manage how and when water is used, so it is common to hear the words water

conservation used synonymously with water efficiency.

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Water Efficiency Approach

Rainwater Harvesting (RWH) Water Recycling Water Efficient Irrigation

Water Efficient Fittings Metering and Leak Detection System

skema soalan final v.2 - bfc315332603

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